Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.41	12.595%	$59.011	$59.01	$59.00	$59.00
Purchase #2	$20.36	3.208%	$21.0131	$21.01	$21.00	$21.00
Purchase #3	$45.69	7.334%	$49.0409	$49.04	$49.05	$49.00
Purchase #4	$145.71	9.684%	$159.8206	$159.82	$159.80	$159.80
Purchase #5	$94.87	11.496%	$105.7763	$105.78	$105.80	$105.80
Purchase #6	$76.79	5.772%	$81.2223	$81.22	$81.20	$81.20
Purchase #7	$85.99	6.856%	$91.8855	$91.89	$91.90	$91.90
7 purchase totals =	$521.82		$567.7697	$567.77	$567.75	$567.70